• Introduction.• Shape Memory Alloy.• Operation principle.• Types of SMA• Ni-Ti Alloy.• Advantages & Disadvantages of Ni-Ti Alloy• Ni-Ti Vs. Copper based SMA.• Ni-Ti Vs. stainless steel.• Applications• References
• Smart materials are designed materials that have one or moreproperties that can be significantly changed in a controlledfashion by external stimuli, suchas stress, temperature, moisture, electric or magnetic fields.• Types of Smart material:• Shape memory alloy• Piezoelectric• Thermoelectric materials• Thermochromic• Photochromic, etc.
• SMA are the Materials which have the ability to return to apredetermined shape when heated or cooled, or below itstransformation temperature.• When it is heated above its transformation temperature itundergoes a change in crystal structure which causes it toreturn to its original shape.• The most common shape memory material is an alloy of nickeland titanium called Nitinol• This particular alloy has very good electrical and mechanicalproperties, long fatigue life, and high corrosion resistance.
• SMA has two stable phases1) Austenite (high temperature phase)2) Martensite (low temperature phase)Fig. 1: Different phases of a shape memory alloy
(a) (b)Fig. 2: (a)Temperature-induced phase transformation of a shape memory alloy withoutmechanical loading. (b) hysteresis curve
• Types of SMA• One way SMA• Cu-Al-Ni Alloy, Ti51Ni49• Two way SMA• Types of Alloys• Ni-Ti• Copper
• The term nitinol is derived from its composition and itsplace of discovery: (Nickel Titanium-Naval Ordnance Laboratory).• Nitinol is actuator, sensor and heater all in one material• Nitinol thin film actuators have attracted significantdevelopment efforts in the recent past years.• Nitinol films normally less than 10m in thickness weredeposited on silicon, glass or polymeric substrates bysputter deposition.
Advantages• Simple training mechanism• High power/weight ratio• Noiseless and silent training• High corrosion resistance• Can be controlled with electrical currentDisadvantages• Highly controlled fabrication process required (1% change incomposition results in 20°C temperature variation)• Low energy conversion efficiency (5%)
• .Ni-Ti based SMA• Recoverable strain(8%)• Shape change temperaturerange (-200 to +200 C)• High resistance to corrosion• Consist of 50% Ni and 50%Ti• Expensive material andhighly controlled Fabricationprocess.Copper based SMA• Recoverable strain(4-5%)• Shape change temperaturerange (-200 to +150 C)• Low resistance tocorrosion.• Consist of 80% Cu and20% Zn+Al.• Less expensive materialand Metallurgical process.
• MEMS electrical & thermal Actuator• Micro-grippers• Aerospace and Naval Applications• Medical• Dentistry• Repair broken bones• Replace damage discs• Cellular phones• Robotics arm• Fire alarm sensor• Arts
• Ackland G. J., “Atomistic modelling of the shape memory effect”, eprintarxiv:condmat/0509456, september 2005• Ming H. Wu and L. Mcd. Schetky,” INDUSTRIAL APPLICATIONS FOR SHAPE MEMORYALLOYS”, proceedings of the international conference on shape memory and superelastictechnolgies, pacific grove, california, P.171-182 (2000).• Milenko braunovic, senior member, ieee, and c. Labrecque,” shape-memory alloy mechanicalcontact devices”, IEEE TRANSACTIONS ON COMPONENTS, PACKAGING, ANDMANUFACTURING TECHNOLOGY-PART A, VOL. 19, no. 3, september 1996• “Shape-memory alloys – metallurgical solution looking for a problem”, metallurgia, vol.51,no. 1, january 1984, pp. 26–29• Wu shanqiang, huang peipei,” A micro wall-climbing robot using shape memory alloy”, 2011second international conference on digital manufacturing & automation.• Chen-luen shih, bo-kuai lai, harold kahn, stephen m. Phillips, senior member, IEEE, and arthurH. Heuer,” A robust co-sputtering fabrication procedure forTini shape memory alloys forMEMS”, IEEE JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 10, no.1, march 2001